The present invention relates to a finned heat exchanger used widely in the field of air-conditioners or refrigerating machines.
Recently, along with the trend for smaller and thinner structures for air-conditioners, a further enhancement of the heat exchange capacity is being demanded in finned heat exchangers.
FIG. 7A and FIG. 7B are plan and sectional views of a prior art finned heat exchanger having an improved heat exchange capacity, which was disclosed in Japanese Laid-Open Patent No. Hei 2-217792. A plurality of fin collars 12 are burred at a right angle to each plate fin 11. The fin collars 12 are spaced at specific intervals on the plate fins. A heat transfer tube 13 is inserted into the fin collars 12, aligned with each other on different plate fins and is expanded to contact tightly within the fin collars 12. Arrow B shows a principal direction of an air stream. Between adjacent fin collars 12 on each plate fin, three rows of raised portion groups 14a, 14b, 14c are formed on one side of each plate fin 11. The three rows of raised portion groups are composed of one raised portion 14a, two raised portions 14b, and three raised portions 14c. The width Wf of a raised portion is formed to be about 1/3 of a flat fin width Wb of a fin between raised portions.
In the finned heat exchanger, shown in FIG. 7A and FIG. 7B, the air flow pressure drop was decreased and the heat exchange capacity was improved. However, if there is a temperature difference between the fluids flowing in the heat transfer tubes 13, heat exchange occurs due to heat conduction through the flat portion of the plate fins in the wide areas thereon. As a result, the improvement in the heat exchange capacity of the Hei application was found to be insufficient. In particular, forming plural rows of heat transfer tubes in the finned heat exchanger shown in FIG. 7A and FIG. 7B, and having fluids flowing in the heat transfer tubes with a temperature difference in the fluids flowing in the heat transfer tubes adjacent in rows, the fluids flowing in the individual heat exchange tubes exchange heat with each other by heat conduction through the flat fin area having a wide area. Accordingly, if the finned heat exchanger in FIG. 7A and FIG. 7B is used in plural rows, the Hei heat exchanger lacks sufficient heat exchange capacity.